The shrieker is a monster in NetHack. According to Dungeons and Dragons, the shrieker is a large purple fungus. While it has no attacks and moves very slowly, its ability to shriek gives it the ability to aggravate monsters and occasionally (1/10 of all shrieks[1]) summon a random monster somewhere on the level, 1/13[2] of which are purple worms (the explanation given for this is that purple worms enjoy consuming shriekers and are attracted by their shriek[3]). #Chatting with a shrieker will also cause it to shriek; this aggravates monsters, but cannot summon any.[4] The shrieker corpse also gives a 20% chance of poison resistance, and is safe to eat; further, as the shrieker is considered a fungus, consuming a shrieker corpse does not break the vegan or vegetarian conducts.

The line "The shrieker shrieks." has gained a reputation as being one of the most memorable lines in NetHack.

SLASH'EM

In SLASH'EM shriekers, like all F except lichens, may rise from the dead. Additionally, they are incapable of summoning purple worms[5] but are slightly more likely to summon a monster with a shriek (1/8 chance instead of 1/10). The first change may be due to the fact that two other monsters, the squealer and the mobat, have the same shriek in SLASH'EM. They are also immune to death rays, strangely enough.

Encyclopedia entry

With a single, savage thrust of her spear, the warrior-woman
impaled the fungus, silencing it. However, it was too late:
the alarm had been raised[...]
Suddenly, a large, dark shape rose from the abyss before them,
its fetid bulk looming overhead...The monster was some kind of
great dark worm, but that was about all they were sure of.